1. Field of the Invention
The present invention relates to a sound device of an expansion station and, more particularly, to a sound device of an expansion station for a notebook personal computer and which removes noise of a sound signal supplied from the personal computer.
Recently, minimum facilities are provided in a notebook personal computer so that the mobility thereof is improved by realizing a compact and thin body. Expanded facilities are provided in an expansion station connectable to the notebook personal computer.
2. Description of the Related Art
FIG. 1 shows a connection between a notebook personal computer and an expansion station.
For example, referring to FIG. 1, a notebook personal computer 10 is connected to an expansion station 20 by a 220-pin connector 15. Various facilities including a CD-ROM device 22, a flexible disk device 24, a sound module (sound device) 26, a LAN module 28, a printer interface 30, a modem interface 32, a CRT interface 34 are provided in the expansion station 20. A printer 36 is connected to the connector 35, a modem 38 is connected to a connector 37, and a CRT display 40 is connected to a connector 39.
The various facilities in the expansion station 20 including the CD-ROM device 22, the flexible disk device 24, the sound module 26, the LAN module 28, the printer interface 30, the modem interface 32, the CRT interface 34 operate according to respective instructions from the notebook personal computer 10. For example, the sound module 26 is supplied with an analog speech signal generated by a sound source circuit built in the notebook personal computer 10 via the connector 15. The sound module 26 amplifies this speech signal using a built-in high-performance amplifier (high-performance as compared to an amplifier built in the notebook personal computer) and causes a high-performance speaker to give an associated sound.
A power supply of a sound source circuit of the notebook personal computer 10 is different from a power supply of the sound module 26 of the expansion station 20. When the notebook personal computer 10 is connected to the expansion station 20, sound noise is generated when there is a potential difference between the power supply voltage levels or between the ground levels. It is also difficult to provide precise impedance matching between the sound source circuit of the notebook personal computer 10 and the sound module 26 of the expansion station 20. Therefore, sound noise occurs due to impedance mismatching. There is a problem in that such sound noise does not stand out while a sound is being produced but is distinctively heard in a silent state.
Japanese Laid-Open Patent No. 58-96448 discloses a device for automatically cutting off a power supply of a device after a predetermined period of time has elapsed since a speech signal is detected to carry no information.
Japanese Laid-Open Patent Application 4-164485 discloses detecting a silence (absence of a received sound) in a call proceeding in a cordless telephone set, generating a control signal in the silence state and cutting off a power supply of the telephone set except that for a silence distinction unit.
When the device described in Japanese Laid-Open Patent No. 58-96448 is applied to the sound module 26 of the expansion station 20, the power supply of the sound module 26 is cut off after a predetermined period of time has elapsed since a silence is detected. There is a problem in that, when a speech signal is supplied from the sound source circuit of the notebook personal computer 10 subsequently, the sound module 26 cannot produce a sound.
When the device described in Japanese Laid-Open Patent No. 4-164485 is applied to the sound module 26 of the expansion station 20, the power supply of the sound module 26 is cut off after a predetermined period of time has elapsed since a silence is detected. There is a problem in that, when a speech signal is supplied from the sound source circuit of the notebook personal computer 10 subsequently, the sound module 26 cannot produce a sound.
Accordingly, an object of the present invention is to provide a sound device in which the aforementioned problems are eliminated.
Another and more specific object of the present invention is to provide a sound device of an expansion station in which noise is prevented from being produced in a silent state, and in which the sound quality in the expansion station is improved.
The aforementioned object can be achieved by a sound device provided in an expansion station for a notebook personal computer and supplied with a sound signal from the personal computer so as to produce a sound, comprising: silent state detecting means for detecting a silent state in the sound signal supplied by the personal computer; and sound production preventing means for preventing a sound from being produced from the sound signal supplied by the personal computer when the silent state is detected by the silent state detecting means.
By preventing a sound from being produced from the sound signal supplied from the personal computer when a silent state is detected by the silent state detecting means, noise is prevented from being produced in a silent state. With this, the sound quality of an expansion station is improved.
The sound device may further comprise:
frequency detecting means for detecting a noise frequency of the sound signal supplied by the personal computer when the silent state is detected by the silent state detecting means; storage means for storing the noise frequency detected by the frequency detecting means; filter means for attenuating components of the sound signal at a stored noise frequency stored in the storage means, when the silent state is not detected.
By detecting a noise frequency of the sound signal supplied from the personal computer in a silent state and by attenuating components at the noise frequency in the sound signal supplied from the personal computer when a sound is being produced, noise is removed from the sound derived from the sound signal supplied from the personal computer.
The sound device may further comprise: output amplifying means for amplifying the sound signal for the purpose of sound production; and detection amplifying means for amplifying the sound signal for the purpose of detecting the silent state.
By providing the detection amplifying means for amplifying the sound signal for the purpose of detecting a silent state, in addition to the output amplifying means for amplifying the sound signal for the purpose of sound production, the silent state can be detected with a high precision by controlling the degree of amplification by the detection amplifying means.
The sound device may further comprise switch means for suspending a power supply to the output amplifying means and the filter means, when the silent state detecting means detects the silent state.
By preventing a power supply to the output amplifying means and the filter means when the silent state is detected by the silent state detecting means, power consumption in the silent state is reduced.
The sound device may further comprise switch means for preventing a supply of the sound signal output by the detection amplifying means to the silent state detecting means, when a silent state is not detected.
By preventing the sound signal output by the detection amplifying means from being supplied to the silent state detecting means when the silent state is not detected, the sound signal at an excessively high level is prevented from being supplied to the silent state detecting means when a sound is being produced.